1. Field of the Invention
The present invention relates to a line backup method and system in an ATM (Asynchronous Transfer Mode) network and, more particularly, to a line switchover method and a system for performing line switchover in the event of a line failure between exchange units.
2. Description of the Related Art
In a traditional line backup method provisioned for a line failure between ATM exchange units or in an ATM communication network, line switchover has been performed by detecting a failure at the physical layer. In such a switchover method, switchover control is generally performed for each physical line between the exchange units at both ends of the connection, and switchover involving a third exchange unit cannot be carried out.
A connection-by-connection switchover control method for Virtual Channels (VCs) is disclosed in Japanese Unexamined Patent Publication No. 9-93260. However, since this method uses a VC AIS (Alarm Indication Signal) OAM cell to detect the occurrence of a failure and switch the connection, if transmission/reception of the OAM signal becomes impossible because of the failure, the switchover operation cannot be performed.
This method, therefore, cannot handle logical failures (e.g., software failure) occurring within an exchange unit. It is also not possible to provide for voluntary switchover performed through maintenance and administration operations from a maintenance console, etc. If a connection between exchange units is to be switched manually, the only possible way is to issue a command to switch the connection from each of the maintenance consoles connected to the exchange units at both ends, and it is, therefore, not possible to switch the connection in a synchronized fashion between the exchange units.
Furthermore, connection-by-connection switchover control is usually implemented in software. Since OAM cells for all the VC connections set up along the line arrive at the switching end station, regardless of whether the connection is a connection to be switched or not, the end station must process all of these OAM cells, and the processing logic becomes complex, involving the problem of increased processing burden and increased delay.